Separation of a sour syngas stream

ABSTRACT

A feed stream, comprising hydrogen sulphide (H 2 S), carbon dioxide (CO 2 ), hydrogen (H 2 ) and, optionally, carbon monoxide (CO), is separated into at least a CO 2  product stream and an H 2  or H 2  and CO product stream. The stream is separated using a pressure swing adsorption system, an H 2 S removal system and a further separation system, which systems are used in series to separate the stream. The method has particular application in the separation of a sour (i.e. sulphur containing) syngas, as for example produced from the gasification of solid or heavy liquid carbonaceous feedstock.

BACKGROUND OF THE INVENTION

The present invention relates to a method for separating a feed stream,comprising hydrogen sulphide (H₂S), carbon dioxide (CO₂), and one orboth of hydrogen (H₂) and carbon monoxide (CO), into at least a CO₂product stream and an H₂ or H₂ and CO product stream. The invention hasparticular application in the separation of a sour (i.e. sulphurcontaining) syngas, as for example may be obtained from the gasificationof solid or liquid carbonaceous feedstock, to obtain: a CO₂ rich productstream suitable for geological storage; an H₂ or H₂ and CO productstream suitable for use in a chemicals plant or refinery, or as fuel fora gas turbine; and, optionally but preferably, an H₂S enriched streamthat can be further processed, e.g. in a Claus unit or other suitablesulphur recovery system, in order to convert to elemental sulphur theH₂S contained therein.

It is well known that streams comprising H₂ and CO can be produced viagasification of solid or liquid feedstock. However, such processesresult in a crude syngas stream containing, in addition to H₂ and CO,also CO₂ and H₂S. The CO₂ arises from the partial combustion of thefeedstock during gasification, the concentration of which is increasedif the crude syngas steam is subjected to a water-gas shift reaction toconvert by reaction with H₂O all or part of the CO in the stream to CO₂and H₂. The H₂S arises from the reduction of sulphur present in thefeedstock during gasification, and from further conversion of othersulphur species in the crude syngas stream to H₂S during the water-gasshift reaction.

Due to concerns over greenhouse gas emissions, there is a growing desireto remove CO₂ from syngas prior to its use (e.g. as a combustion fuel).The CO₂ may be compressed so as to be stored underground. H₂S must alsobe removed from the syngas as it could be a poison for downstreamprocesses, or if the syngas is combusted in a gas turbine then the H₂Sis converted into SO₂, which has limits on its emission and so wouldneed to be removed using expensive desulphurization technology on thecombustion exhaust gas.

After separating the H₂S and CO₂ from the syngas, it may not bepractical or permissible to store the H₂S with the CO₂. Therefore asolution must also be found for cost effective removal of the H₂S fromthe CO₂ before pipeline transportation.

The currently used commercial solution for this problem is to use aliquid absorption process (e.g. Selexol™, Rectisol® or other such acidgas removal process) that removes the CO₂ and H₂S from the syngas. TheCO₂ is obtained as a product gas of sufficient purity that it can bedirectly pressurized and piped to storage or enhanced oil recovery(EOR). The H₂S is obtained as an H₂S enriched mixture comprising 20-80mole % H₂S, which mixture can then be sent to, for example, a Claus unitto produce elemental sulphur. However, such liquid adsorption processesare costly (both in terms of capital and operating cost) and havesignificant power consumption.

US-A1-2007/0178035 describes a method of treating a gaseous mixturecomprising H₂, CO₂ and at least one combustible gas selected from thegroup consisting of H₂S, CO and CH₄. H₂ is separated from the gaseousmixture, preferably by a pressure swing adsorption (PSA) process, toproduce a separated H₂ gas and a crude CO₂ gas comprising thecombustible gas(es). The crude CO₂ gas is then combusted in the presenceof O₂ to produce heat and a CO₂ product gas comprising combustionproducts of the combustible gas(es). The combustible gas may be H₂S, inwhich case the combustion products are SO₂ and SO₃ (SO_(X)) and H₂O. TheCO₂ product gas can then be washed with water to cool the gas andconvert SO₃ to sulfuric acid, and maintained at elevated pressure in thepresence of O₂, water and NO_(x) to convert SO₂ and NO_(x) to sulfuricacid and nitric acid.

Thus, in the process described in US-A1-2007/0178035, H₂S is removed byconversion to SO_(x) and then H₂SO₄, and is not available for subsequentconversion to elemental sulphur in a Claus unit. Any H₂/CO present inthe crude CO₂ gas is also combusted, and thus lost as potential product.

US-A1-2008/0173585 describes a method of purifying an impure CO₂ streamby partial condensation. The method comprises compressing impure CO₂gas, condensing at least a portion of the compressed gas to produceimpure CO₂ liquid; expanding at least a portion of said impure CO₂liquid to produce expanded impure CO₂ liquid; and separating at least aportion of said expanded impure CO₂ liquid in a mass transfer separationcolumn system to produce a contaminant-enriched overhead vapor and CO₂bottoms liquid. In one embodiment, the impure CO₂ is obtained from wastegas from a hydrogen PSA process, the contaminants removed being H₂, CO,nitrogen, methane and argon. In the embodiment depicted in FIGS. 2 and 3of the document, a temperature swing adsorption (TSA) unit is used toremove water from the impure CO₂ stream prior to the partialcondensation process, so as to prevent water from freezing and blockingthe heat exchanger.

US-A1-2008/0173584 describes a similar method to that described inUS-A1-2008/0173585.

US-A1-2007/0232706 describes a method of producing a carbon dioxideproduct stream from a hydrogen plant. In one embodiment, a vacuumpressure swing adsorption (VPSA) unit is used to separate a crude CO₂stream from at least part of a syngas stream from a steam-methanereformer. The crude CO₂ is compressed, passed through a temperaturepressure swing adsorption (TPSA) unit to dry the stream, and partiallycondensed and distilled to obtain liquid CO₂ product stream, a CO₂ richvapour, and a CO₂ depleted vapour, the latter being recycled to the VPSAunit.

Chemical Engineering Journal 155 (2009) 594-602, “Desulfurization of airat high and low H₂S concentrations”, describes the capability toseparate H₂S from air using adsorption on activated carbon. It alsodescribes a potential advantage of the presence of water vapour in thefeed stream in enhancing H₂S uptake for at least one type of modifiedactivated carbon.

Adsorption 15 (2009) 477-488, “Enhanced removal of hydrogen sulfide froma gas stream by 3-aminopropyltriethoxysilane-surface-functionalizedactivated carbon”, describes the capability to separate H₂S from Claustail gas using adsorption on activated carbon. This document alsosuggests that for some carbon adsorbents, the presence of water in thefeed stream may enhance the H₂S capacity.

US-B2-7306651 describes the separation of a gas mixture comprising H₂Sand H₂ using the combination of a PSA unit with a membrane. The PSAseparates the feed stream into a H₂ stream and two H₂S-rich streams. OneH₂S-rich stream is recovered as product and the second is compressed andput through a membrane to remove the H₂. The H₂S is then supplied to thePSA unit at pressure for rinsing and the H₂ returned to the PSA unit forpurging.

EP-B1-0444987 describes the separation of CO₂ and H₂S from a syngasstream produced by gasification of coal. The syngas stream, containingH₂S, is reacted with steam in a catalytic CO-shift reactor to convertessentially all the CO in the stream to CO₂. The stream is sent to a PSAunit that adsorbs CO₂ and H₂S in preference to H₂, to separate thestream into an H₂ product gas and a stream containing CO₂ and H₂S. Thestream containing CO₂ and H₂S is sent to a second PSA unit that adsorbsH₂S in preference to CO₂, to provide a CO₂ product, stated to be of highpurity, and a H₂S containing stream, which is sent to a Claus unit forconversion of the H₂S into elemental sulphur.

There is a continuing need for new methods of separating sour syngasstreams, and other streams comprising H₂S, CO₂, H₂ and optionally CO. Inparticular, there is a need for methods that can, preferably at lowercost and/or with lower power consumption than the current commerciallyused methods, separate such streams to obtain: an H₂ or H₂ and COproduct of sufficient purity for refinery, chemicals or powerapplications; a CO₂ product of suitable purity for geological storage orEOR; and, preferably, a H₂S containing product of suitable compositionfor further processing in a sulphur recovery system to convert the H₂Sto elemental sulphur.

BRIEF SUMMARY OF THE INVENTION

According to the present invention, there is provided a method andapparatus for separating a feed stream, comprising H₂S, CO₂, H₂ andoptionally CO, into at least a CO₂ product stream and an H₂ or H₂ and COproduct stream (referred to herein as the “H₂/CO product stream”),wherein the feed stream is separated using a pressure swing adsorptionsystem (referred to herein as the “H₂/CO-PSA system”), an H₂S removalsystem, and a further separation system, and wherein:

the feed stream is introduced into either the H₂/CO-PSA system or theH₂S removal system;

the H₂/CO-PSA system either separates the feed stream to provide theH₂/CO product stream and a stream enriched in CO₂ and H₂S, or separatesa stream already depleted in H₂S by the H₂S removal system to providethe H₂/CO product stream and a stream enriched in CO₂ and depleted inH₂S;

the H₂S removal system either processes the feed stream to provide astream depleted in H₂S, or processes a stream already enriched in CO₂and H₂S by the H₂/CO-PSA system to provide a stream enriched in CO₂ anddepleted in H₂S, or processes a stream already enriched in CO₂ and H₂Sby the H₂/CO-PSA system and further enriched in CO₂ and H₂S by thefurther separation system to provide the CO₂ product stream; and

the further separation system either separates a stream already enrichedin CO₂ and H₂S by the H₂/CO-PSA system to provide a stream furtherenriched in CO₂ and H₂S and a stream comprising H₂ or H₂ and CO, orseparates a stream already enriched in CO₂ by the H₂/CO-PSA system anddepleted in H₂S by the H₂S removal system to provide the CO₂ productstream and a stream comprising H₂ or H₂ and CO.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a flow sheet depicting an embodiment of the present invention;

FIG. 2 is a flow sheet depicting an exemplary rinse design for thesour-PSA system;

FIG. 3 is a flow sheet depicting another rinse design for the sour-PSAsystem;

FIG. 4 is a flow sheet depicting another rinse design for the sour-PSAsystem;

FIG. 5 is a flow sheet depicting another embodiment of the presentinvention; and

FIG. 6 is a flow sheet depicting a further embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The method of the present invention comprises separating a feed stream,comprising H₂S, CO₂, H₂ and optionally CO, into at least a CO₂ productstream and an H₂/CO product stream, using an H₂/CO-PSA system, an H₂Sremoval system and a further separation system. These three systems areused in series to separate the feed stream, such that the feed stream isfirst separated/processed in one of said systems (more specifically, ineither the H₂/CO-PSA system or the H₂S removal system), aseparated/processed portion of the feed obtained from said first one ofsaid systems is sent to a second one of said systems, and a furtherseparated/processed portion of the feed obtained from said second one ofsaid systems is sent to the final one of said systems.

The H₂/CO-PSA system either separates the feed stream to provide theH₂/CO product stream and a stream enriched in CO₂ and H₂S, or separatesa stream already depleted in H₂S by the H₂S removal system to providethe H₂/CO product stream and a stream enriched in CO₂ and depleted inH₂S. The H₂/CO-PSA system therefore either receives the feed stream, oris located downstream of the H₂S removal system.

The H₂S removal system either processes the feed stream to provide astream depleted in H₂S, or processes a stream already enriched in CO₂and H₂S by the H₂/CO-PSA system to provide a stream enriched in CO₂ anddepleted in H₂S, or processes a stream already enriched in CO₂ and H₂Sby the H₂/CO-PSA system and further enriched in CO₂ and H₂S by thefurther separation system to provide the CO₂ product stream. The H₂Sremoval system may therefore receive the feed stream, or may be locateddownstream of either or both of the H₂/CO-PSA system and the CO₂separation system. Preferably, the H₂S removal system separates the feedstream, or said stream already enriched in CO₂ and H₂S by the H₂/CO-PSAsystem, or said stream already enriched in CO₂ and H₂S by the H₂/CO-PSAsystem and further enriched in CO₂ and H₂S by the further separationsystem, to provide an H₂S enriched stream in addition to providing saidstream depleted in H₂S, said stream enriched in CO₂ and depleted in H₂S,or said CO₂ product stream. In particular, the H₂S removal system ispreferably another pressure swing adsorption system (referred to hereinas the “sour-PSA system”). If desired, one or more H₂S containingstreams, such as the tail-gas from a Claus unit and/or the off-gas froma sour water stripper, could be combined with or concurrently introducedalongside the stream fed into and processed by the H₂S removal system.

The further separation system either separates a stream already enrichedin CO₂ and H₂S by the H₂/CO-PSA system to provide a stream furtherenriched in CO₂ and H₂S and a stream comprising H₂ or H₂ and CO, orseparates a stream already enriched in CO₂ by the H₂/CO-PSA system anddepleted in H₂S by the H₂S removal system to provide the CO₂ productstream and a stream comprising H₂ or H₂ and CO. Thus, the furtherseparation system is always positioned downstream of the H₂/CO-PSAsystem, and may be upstream or downstream of the H₂S removal system. Thefurther separation system is positioned downstream of the H₂/CO-PSAsystem so that it receives a stream that has already been enriched inCO₂ or CO₂ and H₂S by the H₂/CO-PSA system (bulk separation of at leastCO₂ from H₂ or H₂ and CO therefore taking place in the H₂/CO-PSAsystem). This, in turn, improves the level of separation of CO₂ or CO₂and H₂S from H₂ or H₂ and CO achievable within the separation system.The further separation system may, for example, be a partialcondensation system or a membrane separation system.

The methods according to the present invention provide an alternative tothe current commercially used methods for separating sour syngas andsimilar H₂S containing streams, whereby the sour syngas or other suchfeed is separated into separate H₂S, CO₂ and H₂ streams by a liquidabsorption process, such as for example Selexol™ or Rectisol®, only.

In the context of the method and apparatus of the present invention, andunless otherwise indicated, all references herein to a stream beingenriched or depleted in a component refer to said stream being enrichedor depleted in said component relative to the feed stream (i.e., where astream is enriched in a component the concentration (mole percentage) ofthat component in said stream is greater than the concentration of thatcomponent in the feed stream, and where a stream is depleted in acomponent the concentration of that component in said stream is lessthan the concentration of that component in the feed stream).

The feed stream (also referred to hereinafter as the “process feed”)comprises at least H₂S, CO₂, and H₂, and typically further comprises atleast some CO. It is, preferably, formed from a syngas stream obtainedfrom gasification of solid (e.g. coal, petcoke, biomass, municipalwaste) or liquid (in particular a heavy liquid, e.g. asphaltenes)carbonaceous feedstock. The feed stream may be a syngas stream that hasbeen further treated to remove particulates and/or alter the ratio of H₂to CO, by techniques known in the art. For example, a water wash stepwill typically have been employed to remove the majority ofparticulates, and a water-gas shift reaction may have be used to convertsome, most or all of the CO present in the crude syngas to H and CO₂.Other impurities may be present, such as CH₄, N₂ and/or Ar which willusually be separated alongside the H₂. Other sulphur containingcomponents (e.g. COS) may also be present in the feed stream, in whichcase these components preferably are removed/separated alongside H₂Ssuch that, preferably, any streams depleted in H₂S are depleted in saidother sulphur containing components also. Water may be present in thefeed stream, or a dry feed stream may be used (which may have been driedusing techniques known in the art).

The feed stream preferably comprises: from about 500 ppm (0.05 mole %)to about 5 mole %, more preferably from about 2000 ppm (0.2 mole %) toabout 2 mole % H₂S (or H₂S and any other sulphur containing components);from about 10 to about 60 mole %, more preferably from about 35 to about55 mole % CO₂; and from about 35 mole % to the remainder (i.e. 100 mole% less the mole % of H₂S and CO₂) of H₂ or a mixture of H₂ and CO, morepreferably from about 40 mole % to the remainder of H₂ or a mixture ofH₂ and CO.

Prior to introduction into the H₂/CO-PSA system or H₂S removal system,the feed stream may be cooled by indirect heat exchange with, forexample, a stream from said H₂/CO-PSA system and/or a stream from saidH₂S removal system that is at a lower temperature than the feed stream.Examples of such streams (i.e. streams of lower temperature availablefrom the H₂/CO-PSA system or H₂S removal system) may include the CO₂ orCO₂ and H₂S enriched stream from the H₂/CO-PSA system and/or the H₂Senriched stream (where such a stream is produced) from the H₂S removalsystem. Where the CO₂ or CO₂ and H₂S enriched stream from the H₂/CO-PSAsystem is so used, such heat exchange would normally take place prior toany compression of said stream. The cooling can remove water from thefeed stream and if fed to the H₂/CO-PSA system, or to an H₂S removalsystem that employs an adsorbent, may increase adsorption capacity inthe system into which the feed stream is introduced.

The H₂/CO-PSA system may comprise a plurality of adsorbent beds, as isknown in the art. For example, the system may comprise a plurality ofbeds, with the PSA cycles of the individual beds being appropriatelystaggered so that at any point in time there is always at least one bedundergoing adsorption and at least one bed undergoing regeneration, suchthat the system can continuously separate the stream fed to it. Thesystem could also, for example, alternatively or additionally comprisemore than one bed arranged in series and undergoing adsorption at thesame time, the gas passing through one bed being passed to the next bedin the series, and with gases desorbed from the beds during regenerationbeing appropriately combined.

The H₂/CO-PSA system comprises adsorbent selective for at least CO₂ overat least H₂ (i.e. that adsorbs at least CO₂ preferentially to at leastH₂, or, to put it another way, that adsorbs at least CO₂ with greateraffinity than at least H₂). Where the feed stream is fed to theH₂/CO-PSA system, such that the H₂/CO-PSA system is to provide a streamenriched in CO₂ and H₂S, then the H₂/CO-PSA system comprises adsorbentselective for at least CO₂ and H₂S (and, preferably, any other sulphurcontaining components present in the feed) over at least H₂. Where astream already depleted in H₂S by the H₂S removal system is fed to theH₂/CO-PSA system then the H₂/CO-PSA system may not require adsorbentselective also for H₂S (and any other sulphur containing components),although such adsorbent may still be employed, if desired. Where thefeed stream also contains CO then the H₂/CO-PSA system may compriseadsorbent selective for at least CO₂ over both H₂ and CO, or the systemmay comprise adsorbent selective for at least CO₂ and CO over H₂,depending on whether the H₂/CO product stream is, respectively, to beenriched in both H₂ and CO or in H₂ only. It is generally preferred,however, that where the feed stream contains also CO then the H₂/CO-PSAsystem comprises adsorbent selective for at least CO₂ over both H₂ andCO so that the H₂/CO product stream is enriched in both H₂ and CO. Thisis particularly the case where the feed stream contains more than minoramounts of CO. Thus, it is preferred that the H₂/CO-PSA system comprisesadsorbent selective for both CO and CO₂ over H₂, so that the is H₂/COproduct stream is enriched in H₂ but not CO, only where the feed streamcontains a CO concentration of at most about 5 mole %, more preferablyof at most about 2 mole %, and most preferably of at most about 1 mole%.

The H₂/CO-PSA system may comprise a single type of adsorbent, selectivefor all the components that are to be selectively adsorbed by saidsystem, or more than one type of adsorbent that in combination providethe desired selective adsorption. Where more than one type of adsorbentis present, these may be intermixed and/or arranged in separatelayers/zones of a bed, or present in separate beds arranged in series,or arranged in any other manner as appropriate and known in the art.Exemplary adsorbents include carbons, aluminas, silica gels andmolecular sieves. Where the H₂/CO-PSA system is to selectively adsorbH₂S (in addition to at least CO₂), the preference is to use a singlelayer of silica gel if the H₂/CO product requirement is a H₂ and COmixture, a single layer of silica gel or a silica gel/carbon split ifthe H₂/CO product requirement is gas turbine grade H₂, and a silicagel/carbon/5A zeolite split if the H₂/CO product requirement is highpurity H₂. A suitable type of silica gel for use as an adsorbent is, forexample, the high purity silica gel (greater than 99% SiO₂) described inUS-A1-2010/0011955, the disclosure of which is incorporated herein byreference. Where the H₂/CO-PSA system does not need to selectivelyadsorb H₂S (because this has already been removed by the H₂S removalsystem) then zeolite or activated carbon based adsorbents may bepreferable.

The H₂/CO-PSA system may, for example, be operated in the same way asknown PSA systems for separating H₂ from a feed stream, with all knowncycle options appropriate to this technology area (e.g. cycle and steptimings; use, order and operation of adsorption, equalization,repressurisation, depressurisation and purge steps; and so forth). ThePSA cycle employed will, of course, typically include at least anadsorption step and blowdown/depressurisation and purge steps. Duringthe adsorption step the stream to be separated is fed atsuper-atmospheric pressure to the bed(s) undergoing the adsorption stepand CO₂ and any other components that are to be selectively adsorbed,e.g. H₂S and/or CO, are selectively adsorbed from the stream, the gaspushed through the bed(s) during this step forming all or at least aportion of the H₂/CO product stream withdrawn from the H₂/CO-PSA system.During the blowdown/depressurisation step(s) and purge step the pressurein the bed(s) is reduced, and a purge gas passed through the bed(s), todesorb CO₂ and any other components adsorbed during the previousadsorption step, thereby providing gas enriched in CO₂ and any otherselectively adsorbed components, at least a portion of which forms atleast a portion of the stream enriched in CO₂ or CO₂ and H₂S withdrawnfrom the H₂/CO-PSA system, and regenerating the bed(s) in preparationfor the next adsorption step.

The adsorption step may, for example, be carried out at a pressure ofabout 1-10 MPa (10-100 bar) absolute and at a temperature in the rangeof about 10-60° C. In this case, the H₂/CO product stream will,therefore, be obtained at about this pressure and temperature. The CO₂or CO₂ and H₂S enriched stream would typically all be obtained at aboutatmospheric pressure or at pressures slightly above atmospheric, i.e. atabout or slightly above 0.1 MPa, but could be obtained at anything up toabout 0.5 MPa (5 bar) absolute, for example.

The H₂/CO-PSA system may employ a PSA cycle that includes a rinse stepin which the bed(s) undergoing the rinse step are rinsed with gasobtained from one or more other beds of the PSA system during theblowdown and/or purge steps, so that the CO₂ or CO₂ and H₂S enrichedstream produced by the system contains an increased concentration of CO₂and any other components (e.g. H₂S) more strongly adsorbed by thesystem, and a reduced concentration of H₂ and any other components lessstrongly adsorbed by the system. Methods of employing a rinse step in aPSA cycle to increase the concentration of the more adsorbablecomponent(s) in a desorbed gas stream from a PSA system are, forexample, described in U.S. Pat. No. 3,797,201, U.S. Pat. No. 4,171,206and/or U.S. Pat. No. 4,171,207, the disclosures of which areincorporated herein by reference.

If desired, the H₂/CO-PSA system may be a vacuum pressure swingadsorption (VPSA) system, in which the blowdown/depressurization stepand purge step of the PSA cycle are conducted down to and at(respectively) sub-atmospheric pressure, for example down to about 0.01MPa (0.1 bar) absolute. The VPSA system could, for example, be operatedas described in US-A1-2007/0232706, the disclosure of which isincorporated herein by reference. Use of a VPSA system instead of aconventional PSA system may improve the performance of the system, butit would also add cost and would introduce the possibility of O₂contamination resulting from air ingress.

Where the process feed contains CO and is to be introduced into theH₂/CO-PSA system, the H₂/CO-PSA system may also effect a SEWGS(sorption-enhanced water gas shift) reaction as, for example, describedin US-B2-7354562, the disclosure of which is incorporated herein byreference. In this process the PSA system effects a water-gas shiftreaction at the same time as adsorbing CO₂, CO₂ produced by shiftreaction being adsorbed (alongside existing CO₂ in the feed) as it isproduced, thereby driving the conversion of further CO in the feed intoadditional CO₂ and H₂. This process may be carried out at 200° C.-500°C. feed temperature, using an adsorbent such as hydrotalcite or doublesalts (as described in US-B2-7354562). The CO₂ or CO₂ and H₂S enrichedstream produced by the system would typically then be cooled prior toany compression thereof.

Where the H₂/CO-PSA system is a SEWGS system, the hot CO₂ or CO₂ and H₂Senriched stream could also be expanded to sub atmospheric pressure. Thenany steam in the stream could then be condensed out and removed, priorto the stream being recompressed. The expansion step could provide powerfor the compression step (for example by having the expander andcompressor on the same drive shaft).

The H₂/CO product stream is (as noted above) obtained from the H₂/CO-PSAsystem and is enriched in H₂ relative to the feed stream. Where the feedstream contains also CO, the H₂/CO product stream will typically containalso some CO and (as also noted above) in general, and in particularwhere the feed stream contains more than minor amounts of CO, willpreferably also be enriched in CO relative to the feed stream. The H₂/COproduct stream is depleted in both CO₂ and H₂S.

Preferably, at least about 80%, more preferably at least about 85%, andmore preferably at least about 95% of the H₂ present in the feed streamis recovered in the H₂/CO product stream. Where the feed stream containsalso CO and the H₂/CO product stream is also enriched in CO then,preferably, at least about 75%, more preferably at least about 80%, andmost preferably at least about 90% of the H₂ and CO (in combination)present in the feed stream is recovered the H₂/CO product stream.Preferably at most about 25%, and more preferably at most about 15% ofthe CO₂ present in the feed stream is recovered the H₂/CO productstream, and most preferably no or substantially no CO₂ is recovered inH₂/CO product stream (i.e. the H₂/CO product stream is free orsubstantially free of CO₂). The percentage recovery in the H₂/CO productstream of a component or combination of components can be calculatedfrom the moles of the component or components in question in the feedand H₂/CO product streams. Thus, if for example the feed were tocomprise 50 kmol/hr of CO₂, 25 kmol/hr of H₂ and 25 kmol/hr of CO; andthe H₂/CO product stream were to contain 5 kmol/hr of CO₂, 23 kmol/hr ofH₂ and 20 kmol/hr of CO; then in this case 10% of the CO₂, 92% of the H₂and 86% of the H₂ and CO present in the feed stream would be recoveredin the H₂/CO product stream.

Preferably, the H₂/CO product stream contains at most about 50 ppm andmore preferably at most about 10 ppm H₂S (or H₂S and any other sulphurcontaining components), and most preferably is free of H₂S (and anyother sulphur containing components). The H₂/CO product stream may, asnoted above, still contain impurities such as CH₄, N₂ and/or Ar.Alternatively, the H₂/CO product stream may be a substantially pure orpure stream of H₂ or H₂ and CO.

The H₂/CO product stream may for example be a H₂-rich gas of sufficientpurity to be sent to a gas turbine as fuel, or a H₂ product ofsufficient purity for refinery and chemicals applications.

Alternatively, and in particular where the feed stream contains CO inmore than minor amounts, the H₂/CO product may for example be mixture ofH₂ and CO having a specific ratio of H₂ and CO desired for use as feedto a chemicals plant, such as a Fisher-Tropsch plant or methanol plant.

Prior to such uses of the H₂/CO product stream, the stream may also beheated and expanded to make power.

If the H₂/CO product stream comprises a mixture of H₂ and CO then afurther potential use of the stream may be to send the product stream toa partial condensation system to further split the stream into a numberof fractions of different composition.

As noted above, the H₂/CO-PSA system also provides a stream enriched inCO₂. Where this stream is obtained from the H₂/CO-PSA system separatingthe feed stream then this stream is also enriched in H₂S, and where thisstream is obtained from the H₂/CO-PSA system separating a stream alreadydepleted in H₂S by the H₂S removal system then this stream is likewisedepleted in H₂S. Due to complete separation of all H₂ and/or CO from allCO₂ by the H₂/CO-PSA system not being economically viable, the CO₂enriched stream produced by the H₂/CO-PSA system will also contain acertain amount of H₂ and (if also present in the feed stream) CO.Preferably, the CO₂ enriched stream produced by the H₂/CO-PSA system hasa CO₂ concentration of at least about 60 mole %, more preferably atleast about 70 mole %, more preferably at least about 80 mole %. Wherethe CO₂ enriched stream is depleted in H₂S, the H₂S concentration (orconcentration of H₂S and any other sulphur containing components) of thestream is preferably about 100 ppm or less, more preferably about 50 ppmor less, more preferably about 20 ppm or less, and most preferably thestream is free of H₂S (and any other sulphur containing components).Where the CO₂ enriched stream is enriched in H₂S then preferably all orsubstantially all of the H₂S, and preferably all or substantially all ofany other sulphur containing components, present in the feed stream isrecovered in this CO₂ enriched stream.

The CO₂ enriched (and H₂S enriched or depleted) stream obtained from theH₂/CO-PSA system will typically need to be compressed. In particular,compression is likely to be necessary if the stream is to be nextprocessed in the H₂S removal system, and may likewise be necessary wherethe stream is to be next separated in the further separation system(such as where said further separation system is a partial condensationor membrane separation system). Multi-stage compression withintercooling and water knock-out may be used. The CO₂ or CO₂ and H₂Senriched stream could be composed of more than one stream removed fromthe H₂/CO-PSA system at different pressure levels. In this case, thedifferent pressure streams could be put into the compressor at theappropriate compression stage to minimise the overall compression power.

The H₂S removal system may be of any type suitable for processing thefeed stream, a stream already enriched in CO₂ and H₂S by the H₂/CO-PSAsystem, or a stream already further enriched in CO₂ and H₂S by thefurther separation system, to remove H₂S (and, preferably, any othersulphur containing components) therefrom and provide, respectively, astream depleted in H₂S, a stream enriched in CO₂ and depleted in H₂Srelative to the feed stream, or the CO₂ product stream.

A relatively simple H₂S removal system that could be used would be adisposable adsorbent system (e.g. a packed bed of ZnO) that would bedisposed of and replaced when saturated with H₂S (although, from aneconomics standpoint, such a system would preferably only be adoptedwhen the concentration of H₂S in the feed stream is relatively low, e.g.less than about 200 ppm). Alternatively, an absorption based system(e.g. Selexol™ or Rectisol®) could be used as the H₂S removal system(use of such a system as the system for removing H₂S still providingcapital and operating cost benefits, due to reduced unit size andassociated power consumption, over the use of such a system to effectalso bulk separation of CO₂ from H₂ or H₂ and CO, as typically done incurrent commercially used methods for separating sour syngas). Anotheroption would be to use as the H₂S removal system a system that directlyconverts to and removes as sulphur the H₂S in the stream received by theH₂S removal system, such a system being for example as described in U.S.Pat. No. 6,962,683, the disclosure of which is incorporated herein byreference.

In preferred embodiments, however, the H₂S removal system is a sour-PSAsystem, which processes the feed stream, stream already enriched in CO₂and H₂S by the H₂/CO-PSA system, or stream already further enriched inCO₂ and H₂S by the further separation system, to remove H₂S (and,preferably, any other sulphur containing components) therefrom byseparating said stream to provide a stream enriched in H₂S in additionto providing said stream depleted in H₂S, said stream enriched in CO₂and depleted in H₂S, or said CO₂ product stream.

Like the H₂/CO-PSA system, the sour-PSA system may comprise a pluralityof adsorbent beds, and/or may comprise a single type of adsorbent,selective for all the components that are to be selectively adsorbed bysaid system, or more than one type of adsorbent that in combinationprovide the desired selective adsorption. The sour-PSA system containsadsorbent selective for H₂S (and, preferably, any other sulphurcomponents, such as COS, that may be present in the stream separated bythe sour-PSA system) over CO₂ and, if present in the stream to beseparated by the sour-PSA system, H₂ and CO. Exemplary adsorbentsinclude silica gels, activated carbons, and molecular sieves. Apreferred option is to use a surface modified or impregnated activatedcarbon, which maximizes the H₂S/CO₂ selectivity of the system. Anotheroption is to include adsorbent, such as an additional layer of silicagel, alumina or molecular sieve (e.g. 4A or 5A), selective for water andother condensables over CO₂ and (if present) H₂ and CO, so that if waterand other condensables are present in the stream fed to the sour-PSAsystem then these components are also selectively adsorbed, with theresult that the H₂S depleted/CO₂ enriched and H₂S depleted/CO₂ productstream obtained from the sour-PSA system is in addition depleted inwater.

During the H₂S removal process, sulphur species including elementalsulphur may form on the adsorbent. Sulphur is known to be capable ofremoving mercury species from a gas and mercury may be present in thestream introduced into the sour-PSA system, in particular where theprocess feed has been generated from gasification of a fossil fuel.Where the process feed contains mercury and the further separationsystem is, for example, a partial condensation system, removal ofmercury upstream of the partial condensation system may be necessary(for example where, as is typical, the CO₂ partial condensation systemuses a heat exchanger that is made of aluminium, which is prone tocorrosion by mercury). Thus, a further benefit of the use of a sour-PSAsystem upstream of the partial condensation system in such anarrangement could be the elimination of the need for a separate sulphurimpregnated carbon bed for mercury removal.

Like the H₂/CO-PSA system, the sour-PSA system may, for example, beoperated in the same way as known PSA systems for separating H₂ from afeed stream, with all known cycle options appropriate to this technologyarea (e.g. cycle and step timings; use, order and operation ofadsorption, equalization, repressurisation, depressurisation, and purgesteps; and so forth). The PSA cycle employed will, of course, typicallyinclude at least an adsorption step and blowdown/depressurisation steps.During the adsorption step the stream to be separated is fed atsuper-atmospheric pressure to the bed(s) undergoing the adsorption stepand H₂S (and any other components to be selectively adsorbed) areselectively adsorbed from the stream, the gas pushed out through thebed(s) during this step forming all or at least a portion of the H₂Sdepleted/CO₂ enriched and H₂S depleted/CO₂ product stream obtained fromthe sour-PSA system. During the blowdown/depressurisation step(s) andpurge step the pressure in the bed(s) is reduced, and a purge gas passedthrough the bed(s), to desorb H₂S and any other components adsorbedduring the previous adsorption step, thereby providing gas enriched inH₂S (and any other selectively adsorbed components), at least a portionof which forms at least a portion of the H₂S enriched stream obtainedfrom the sour-PSA system, and regenerating the bed(s) in preparation forthe next adsorption step.

Alternatively, where the stream to be separated by the sour-PSA systemis in the liquid phase, as may be the case where the further separationsystem is a partial condensation system (as will be described in furtherdetail below) and the sour-PSA system separates a stream already furtherenriched in CO₂ and H₂S by said partial condensation system to providethe CO₂ product stream and a stream enriched in H₂S, then the sour-PSAsystem may be operated in the same way as known PSA systems forseparating a liquid stream, with all known cycle options appropriate tothis technology area. In such circumstances, the PSA cycle employed may,for example, comprise: (a) an adsorption step where the liquid to beseparated is fed to the bed(s) undergoing the adsorption step and H₂S(and any other components to be selectively adsorbed) are selectivelyadsorbed therefrom, the liquid withdrawn from the bed(s) forming all orat least a portion of the CO₂ product stream; (b) a step where liquid isdrained from the bed(s) while supplying a gas (e.g. comprising CO₂ orCO₂ and H₂S) to maintain the pressure inside the bed(s); (c)blowdown/depressurisation step(s) and a purge step where the pressure inthe bed(s) is reduced, and a purge gas passed through the bed(s), todesorb H₂S and any other components adsorbed during the previousadsorption step, thereby providing gas enriched in H₂S (and any otherselectively adsorbed components) at least a portion of which forms atleast a portion of the H₂S enriched stream obtained from the sour-PSAsystem; and (d) a step where the bed(s) are refilled with liquid (e.g.using a portion of the liquid withdrawn during the adsorption stepand/or using the liquid to be separated) thereby pushing out residualgas prior to the next adsorption step.

In either case, the purge gas used during the purge step may, forexample, and as is known in the art, be obtained from the bed(s) of thesour-PSA system during a different step of the PSA cycle (for example, aportion of the gas pushed through the beds during the adsorption stepmay be used as purge gas). Alternatively or additionally, the purge gasmay be obtained from external sources.

For example, steam could be used as a purge gas (either on its own or inaddition with other purge gases) for purging the sour-PSA (which mayimprove removal of H₂S). The purged gas may then be cooled, and watercondensed out, which would increase the H₂S purity of the purge gas.Options for drying the adsorbent bed after purging with steam include:(i) using all or part of the stream comprising H₂ or H₂ and CO obtainedfrom the further separation system; or (ii) using N₂ from an airseparation unit (ASU) and venting the gas.

Equally, some or all of the stream comprising H₂ or H₂ and CO obtainedfrom the further separation system could be used as a purge gas (eitheron its own or in addition with other purge gases) for purging thesour-PSA. The use of this stream as a purge gas will increase theconcentration of H₂ or H₂ and CO in the stream enriched in H₂S obtainedfrom the sour-PSA system (assuming gas obtained during the purge stepforms at least a portion of said stream). This may, however, be ofbenefit where the H₂S enriched stream is to be sent to a Claus unit orother such system that converts H₂S to elemental sulphur via a processthat includes an initial combustion step (the increase in theconcentration of H₂ or H₂ and CO reducing the concentration of H₂Srequired for optimal combustion of the mixture in this initial stepcombustion step).

The purge gas used during the purge step (whether obtained from thebed(s) of sour-PSA or from an external source) may be pre-heated, eitherin part or in full, before it is used for purging the bed(s) of thesour-PSA. The pre-heating may be carried out in an external heater orheat exchanger, using for example an electric heating element, steam, orheat from combustion (e.g. from combustion of all or a portion of theH₂/CO product stream or from combustion of all or a portion of thestream comprising H₂ or H₂ and CO obtained from the further separationsystem). If this approach is chosen then the temperature of the purgegas could for example be raised up to about 300° C., preferably in therange of about 150° C. to about 300° C.

Where the sour-PSA system separates the feed stream, and thus is usedupstream of the H₂/CO-PSA system, the adsorption step used in thesour-PSA system may, for example, be carried out within similar pressureand temperature ranges (i.e. about 1-10 MPa and about 10-60° C.) tothose used for the adsorption step in the H₂/CO-PSA system. Where thesour-PSA system is used downstream of the H₂/CO-PSA system then asomewhat lower pressure range for the adsorption step in the sour-PSAsystem may be preferable. The adsorption may, for example, in the lattercase be carried out at a pressure of 0.5 to 4 MPa (5-40 bar) absolute,more typically at about 3 MPa (30 bar) absolute, and at temperatures ofabout 10-60° C. The H₂S depleted/CO₂ enriched and H₂S depleted/CO₂product stream obtained from the sour-PSA system will, therefore, beobtained at about these pressures and temperatures. The H₂S enrichedstream would typically be obtained at about atmospheric pressure, i.e.0.1 MPa absolute.

Like the H₂/CO-PSA system, the sour-PSA system may be a vacuum pressureswing adsorption (VPSA) system, in which the blowdown/depressurizationstep and purge step of the PSA cycle are conducted at sub-atmosphericpressure. The H₂S enriched stream, which would then be produced atsub-atmospheric pressure, would typically then need to be compressedprior to being sent to a Claus unit or other unit for converting the H₂Sto elemental sulphur.

The sour-PSA system may employ a PSA cycle that includes a rinse step inwhich the bed(s) undergoing the rinse step are rinsed, for example withgas obtained from one or more other beds of the PSA system during theblowdown and/or purge steps, so that the H₂S enriched stream produced bythe system contains an increased concentration of H₂S (and any othersulphur containing components selectively adsorbed by the system). Asnoted above, exemplary methods of employing a rinse step in a PSA cycleto increase the concentration of the more adsorbable component in adesorbed gas stream are described in U.S. Pat. No. 3,797,201, U.S. Pat.No. 4,171,206 and/or U.S. Pat. No. 4,171,207, the contents of which, asnoted above, are incorporated herein by reference. The gas obtained fromsaid one or more other beds undergoing blowdown/purge must be compressedbefore it is used for rinsing, and after compression the gas may becooled and any water present condensed and separated out prior to thegas being used for rinsing.

The rinse gas (i.e., the gas obtained from said one or more other bedsundergoing blowdown/purge that is used in the rinse step) may becompressed to the same pressure as that during the adsorption step, withthe rinse step being carried out on a bed after and at the same pressureas the adsorption step. In this case, the composition of the unadsorbedgas pushed out the bed(s) during the rinse step may be suitable forcombination with the gas pushed out during the adsorption step, in whichcase both gases may be used to form the H₂S depleted/CO₂ enriched andH₂S depleted/CO₂ product stream produced by the sour-PSA system.Alternatively, the rinse gas may be compressed to the pressure after afinal equalization step of the PSA cycle, and supplied after this finalequalization step. The rinse gas could also be compressed to andsupplied at any intermediate pressure. The unadsorbed gas pushed out thebed(s) during the rinse step may also: be fed into another bed of thePSA system just after its purge step, recovering the pressure energy ofthis gas; be used to purge another bed in the PSA system; or be combinedwith the feed to another bed undergoing the adsorption step.

The rinse step may comprise using as a rinse gas a portion of the gasesobtained from both the blowdown and purge steps of the sour-PSA system(the remainder of said gases being, for example, withdrawn to form saidH₂S enriched stream). Alternatively, all or a portion of gas from onlyblowdown or purge steps could be used. For example, in a similar mannerto that described in U.S. Pat. No. 7,306,651, the disclosure of which isincorporated herein by reference, the rinse gas could be obtained fromthe purge step of the PSA cycle, and the H₂S enriched stream obtainedfrom the blowdown step of the PSA cycle. Alternatively, the H₂S enrichedstream could be obtained during the purge step, and rinse gas obtainedfrom the blowdown step.

As noted above, where the H₂S removal system processes the feed streamit provides a stream depleted in H₂S. Preferably, the H₂S concentration(or concentration of H₂S and any other sulphur containing components) insaid H₂S depleted stream is about 100 ppm or less, more preferably about20 ppm or less, more preferably about 5 ppm or less, and most preferablythe stream is free of H₂S (and any other sulphur containing components).Where the H₂S removal system processes a stream already enriched in CO₂and H₂S by the H₂/CO-PSA system, the H₂S removal system provides astream enriched in CO₂ and depleted in H₂S. Preferably, said CO₂enriched and H₂S depleted stream has a CO₂ concentration of at leastabout 60 mole %, more preferably at least about 70 mole %, morepreferably at least about 80 mole %. Preferably, said CO₂ enriched andH₂S depleted stream has an H₂S concentration (or concentration of H₂Sand any other sulphur containing components) of about 100 ppm or less,more preferably about 50 ppm or less, more preferably about 20 ppm orless, and most preferably the stream is free of H₂S (and any othersulphur containing components).

The H₂S enriched stream, where this also is produced by the H₂S removalsystem (such as where the H₂S removal system is a sour-PSA system),typically has an H₂S concentration of at least 4 mole %. Preferably, theH₂S enriched steam is sent or is to be sent to a Claus unit or anothertype of sulphur recovery unit (e.g. LO-CAT®, Selectox) for conversion ofthe H₂S into elemental sulphur, and therefore has a H₂S concentration,such as from about 20 to about 80 mole %, that is suitable for such areaction.

The further separation system, as noted above, separates either a streamalready enriched in CO₂ and H₂S by the H₂/CO-PSA system to provide astream further enriched in CO₂ and H₂S and a stream comprising H₂ or H₂and CO, or separates a stream already enriched in CO₂ by the H₂/CO-PSAsystem and depleted in H₂S by the H₂S removal system to provide the CO₂product stream and a stream comprising H₂ or H₂ and CO. Any type ofsystem suitable for effecting the above-mentioned separation may beused. For example, and as noted above, the further separation system maybe a partial condensation system or a membrane separation system.

In the case of a partial condensation system, the stream to be separatedby the system is cooled and separated into a condensate and a vapour,for example using one or more phase separators and/or distillationcolumns. The heavier components, namely CO₂ and, if present in thestream to be separated, H₂S (and/or other sulphur containingcomponents), are concentrated in the liquid phase, which therefore formsthe stream further enriched in CO₂ and H₂S or the CO₂ product stream.The lighter components, namely H₂ and, if present in the stream to beseparated, CO, are concentrated in the gaseous phase, which thereforeforms the stream comprising H₂ or H₂ and CO (which phase will, however,typically still contain some amount of the heavier components). Partialcondensation processes that are suitable for use in the presentinvention are, for example, described in US-A1-2008/0173585 andUS-A1-2008/0173584, the disclosures of which are incorporated herein byreference.

In the case of a membrane separation system, the stream to be separatedis separated using one or more membranes that have selectivepermeability (i.e. that are more permeable to one or more components ofthe stream to be separated than they are to one or more other componentsof said stream), so as to effect separation of the stream to providesaid stream comprising H₂ or H₂ and CO and said stream further enrichedin CO₂ and H₂S or said CO₂ product stream. For example, membranes may beused that are permeable to H₂ but largely impermeable to CO₂ and/or viceversa, such as are described in Journal of Membrane Science 327 (2009)18-31, “Polymeric membranes for the hydrogen economy: Contemporaryapproaches and prospects for the future”, the disclosure of which isincorporated herein by reference.

Where the further separation system is a partial condensation system, itis important that water and other components that may freeze out (e.g.NH₃ and trace levels of tars) are not present in the stream introducedinto the separation system for separation, or are present insufficiently small amounts (such as, for example, where the stream has adew point of about −55° C. or less) that there is no risk for themfreezing and blocking the heat exchanger of the condensation system(used to cool the stream as necessary for subsequent separation intocondensate and vapour). The presence of water in the stream to beseparated may also be undesirable for other types of further separationsystem. Where the process feed contains water a drying system, such as atemperature swing adsorption (TSA) system or absorptive (e.g. glycol,glycerol) system, may (if desired or necessary) therefore be used at anypoint upstream of the further separation system to ensure that thestream to the further separation system is sufficiently free of water.

For example, a drying system (such as a TSA system) separate from theH₂/CO-PSA system and the H₂S removal system could be used at any pointupstream of the further separation system (e.g. to dry the process feedprior to introduction of the same into the H₂/CO-PSA system or H₂Sremoval system, or to dry the stream obtained from the H₂/CO-PSA systemor, if upstream of the further separation system, the stream obtainedfrom the H₂S removal system) to ensure that the stream to the furtherseparation system is sufficiently free of water. Alternatively oradditionally, if the further separation system is downstream of the H₂Sremoval system then the H₂S removal system may remove water as well asH₂S, such that the stream received by the further separation system issufficiently free of water. For example, where the H₂S removal system isa sour-PSA system the sour-PSA system may, as described above, compriseadsorbent that is selective for water over CO₂ and, if present in thestream separated by the sour-PSA system, H₂ and CO.

Likewise, if the further separation system is a partial condensationsystem that uses an aluminium heat exchanger it may be necessary thatthe stream introduced into the partial condensation system does notcontain any mercury, in which case a sulphur impregnated carbon bedcould be used upstream of the partial condensation system to remove anymercury that may be present, and/or the H₂S removal system may be usedupstream of the condensation system and may be a sour-PSA system thatfunctions to remove also mercury (as described above).

As noted above, where the further separation system separates a streamalready enriched in CO₂ and H₂S by the H₂/CO-PSA system, the furtherseparation system provides a stream further enriched in CO₂ and H₂S(i.e. a stream that is enriched in CO₂ and H₂S relative to the streamalready enriched in CO₂ and H₂S by the H₂/CO-PSA system, and thus thatis further enriched in CO₂ and H₂S relative to the feed stream). Thestream is preferably substantially, and may be entirely, free of H₂ andCO.

As noted above, the CO₂ product stream is obtained either by the H₂Sremoval system processing a stream already enriched in CO₂ and H₂S bythe H₂/CO-PSA system and further enriched in CO₂ and H₂S by the furtherseparation system, or by the further separation system furtherseparating a stream already enriched in CO₂ by the H₂/CO-PSA system anddepleted in H₂S by the H₂S removal system. The CO₂ product stream istherefore both depleted in H₂S relative to the feed stream, enriched inCO₂ relative to the stream already enriched in CO₂ (or in CO₂ and H₂S)by the H₂/CO-PSA system and thus further enriched in CO₂ relative to thefeed stream. Preferably, the CO₂ product stream has an H₂S concentration(or concentration of H₂S and any other sulphur containing components) ofabout 100 ppm or less, more preferably about 50 ppm or less, morepreferably about 25 ppm or less, and most preferably the stream is freeof H₂S (and any other sulphur containing components). Preferably, theCO₂ product stream has a CO₂ concentration of at least about 90%, morepreferably at least about 95%, more preferably at least about 98%. TheCO₂ product stream is preferably substantially, and may be entirely,free of H₂ and CO. The CO₂ product stream may be pure or essentiallypure CO₂.

The CO₂ product stream is preferably compressed, piped and used forenhanced oil recovery (EOR) or sent to geological storage, or is to beused for such purposes, and therefore preferably has a level of puritysuitable for such uses.

The stream comprising H₂ or H₂ and CO obtained from the furtherseparation system will be enriched in H₂ and, if present in the processfeed, CO relative to the stream separated by the further separation, butwill typically still contain some CO₂ and, if present in the streamseparated by the further separation system, H₂S (due to completeseparation of all CO₂ or CO₂ and H₂S from all H₂ or H₂ and CO in thefurther separation system typically not being practical or economicallyviable). The stream comprising H₂ or H₂ and CO recovers sufficient H₂ orH₂ and CO from the stream fed to the further separation system that thestream further enriched in CO₂ and H₂S or the CO₂ product streamproduced by the further separation system is depleted in H₂ or H₂ and COto the desired extent. Typically, this will require the streamcomprising H₂ or H₂ and CO to recovers at least about 95%, and possiblyabout 99% or more the H₂ and (if present) CO present in the stream fedto the further separation system. The stream comprising H₂ or H₂ and COmay be used in a number of ways.

Some or all of said stream comprising H₂ or H₂ and CO may be recycled tothe H₂/CO-PSA system for further separation thereof, thereby increasingthe overall recovery of H₂ or H₂ and CO in the H₂/CO product stream. Forexample, some or all of the stream comprising H₂ or H₂ and CO may becompressed (if and as necessary) and admixed with or introducedconcurrently with the stream sent to the H₂/CO-PSA system for separation(i.e. the process feed, or the H₂S depleted stream obtained from the H₂Sremoval system).

Some or all of said stream comprising H₂ or H₂ and CO may be used as anequalization or repressurisation gas in equalization or repressurisationsteps in of the PSA cycle employed in the H₂/CO-PSA system (which, ascompared to the previous option, may require less compression of thestream).

Some of said stream comprising H₂ or H₂ and CO may be recycled back intothe further separation system for further separation. If the H₂S removalsystem is upstream of the further separation system and said streamcomprising H₂ or H₂ and CO still contains some H₂S then some or all ofsaid stream CO may be recycled to the H₂S removal system for furtherseparation.

Depending upon the level of any CO₂ in the resulting mixture, some orall of said stream comprising H₂ or H₂ and CO could be mixed with aportion or all of the H₂/CO product stream from H₂/CO-PSA system. Where,as is typical, the stream comprising H₂ or H₂ and CO contains some CO₂,combining at least a portion of the H₂/CO product and H₂ or H₂ and COcomprising streams in this way may be used to provide a product streamcatering for chemicals applications in which the presence of some CO₂may be desirable.

As already discussed, where the H₂S removal system is a sour-PSA system,some or all of said stream comprising H₂ or H₂ and CO may be used as apurge gas (either on its own or in addition with other purge gases) forpurging the sour-PSA.

Some or all of said stream comprising H₂ or H₂ and CO may be sent to acombustion system (e.g. a gas turbine, furnace or other suitableapparatus) and combusted to generate useful heat and/or power.

Where said stream comprising H₂ or H₂ and CO does contain CO, some orall of the stream may be combusted in the presence of sufficient O₂ toconvert substantially all H₂ and CO present in the part of the streamcombusted to H₂O to CO₂. The combustion effluent may then be cooled andcompressed to condense out water, which may produce a CO₂ stream ofsufficient purity for compression and geological storage or use in EORalongside the aforementioned CO₂ product stream. Where the streamcomprising H₂ or H₂ and CO contains some H₂S this will converted toSO_(x) by the combustion reaction, and SO_(x) can then be converted toand separated out as sulfuric acid by maintaining the cooled andcompressed combustion effluent at elevated pressure, in the presence ofO₂, water and NO_(x). This process may be conducted as further describedin US-A1-2007/0178035, the disclosure of which is incorporated herein byreference.

Some or all of said stream comprising H₂ or H₂ and CO may simply bevented, flared or otherwise disposed of. Venting or flaring of at leasta portion of said stream may, in particular, be necessary where the feedstream contains additional impurities which otherwise cannot be removed(i.e. because they are not removed alongside H₂S in the H₂S removalsystem, are not separated out with H₂ or H₂ and CO by the H₂/CO-PSAsystem, and are not separated alongside CO₂ in the further separationsystem) and which, if not vented or flared, would build up in thesystems.

Said stream comprising H₂ or H₂ and CO may also be heated and expandedto make power, prior to or as an alternative to any of theaforementioned uses.

As noted at the outset, the H₂/CO-PSA system, H₂S removal system andfurther separation system are arranged such that: the H₂/CO-PSA systemeither receives the feed stream, or is located downstream of the H₂Sremoval system which in that event receives the feed stream; the H₂Sremoval system, if not receiving the feed stream, may be locateddownstream of either or both of the H₂/CO-PSA system and the CO₂separation system; and the further separation system is alwayspositioned downstream of the H₂/CO-PSA system, and may be upstream ordownstream of the H₂S removal system.

Thus, in one embodiment (hereinafter, the “first embodiment”) of themethod of the present invention:

-   -   the feed stream is introduced into the H₂/CO-PSA system;    -   the H₂/CO-PSA system separates the feed stream to provide the        H₂/CO product stream and a stream enriched in CO₂ and H₂S;    -   the H₂S removal system processes said stream enriched in CO₂ and        H₂S to provide a stream enriched in CO₂ and depleted in H₂S; and    -   the further separation system separates said stream enriched in        CO₂ and depleted in H₂S to provide the CO₂ product stream and a        stream comprising H₂ or H₂ and CO.

Further preferred features of this first embodiment, such as use of theH₂S removal system to remove also water, use of a sour-PSA system as theH₂S removal system, uses of the H₂S enriched stream also produced by thesour-PSA system, possible uses of the stream comprising H₂ or H₂ and CO,preferred compositions of the various stream, and so forth, will beapparent from the forgoing general description of the method.

This embodiment provides similar results to the current commerciallyused methods (e.g. Selexol™, Rectisol®) of separating sour syngasstreams, in terms of providing a H₂/CO product forrefinery/chemicals/power applications, a CO₂ product for geologicalstorage or EOR, and optionally a H₂S containing product suitable for usein a Claus reaction, but at lower cost and with lower power requirementsthan said commercially used methods.

In another embodiment (hereinafter, the “second embodiment”) of themethod of the present invention:

-   -   the feed stream is introduced into the H₂S removal system;    -   the H₂S removal system processes the feed stream to provide a        stream depleted in H₂S;    -   the H₂/CO-PSA system separates said stream depleted in H₂S to        provide the H₂/CO product stream and a stream enriched in CO₂        and depleted in H₂S; and    -   the further separation system separates said stream enriched in        CO₂ and depleted in H₂S to provide the CO₂ product stream and a        stream comprising H₂ or H₂ and CO.

Further preferred features of this embodiment will again be apparentfrom the forgoing general description of the method.

As compared to the aforementioned first embodiment, the method accordingto this second embodiment has certain advantages and disadvantages. Thedisadvantages are that: there are, if a sour-PSA system is used as theH₂S removal system, two PSA systems in the H₂/CO product streamproducing line, which may result in an increased pressure drop; theconcentration of H₂S in the feed stream is less than that in the streamto the H₂S removal system in the first embodiment, which makes H₂Sremoval harder; the feed gas volumes are greater, which means largervessel sizes are needed to prevent fluidization; and, where a H₂Sremoval system is used that also produces an H₂S enriched stream, thereis likely to be a relatively greater amount of H₂ or H₂ and CO in theH₂S enriched stream (and thus potentially lost as H₂ and/or CO product).The advantages are that: H₂S is reduced in the CO₂ enriched streamproduced from the H₂/CO-PSA system, which therefore does not need to berecompressed in any recompression of this stream prior to furtherseparation in the further separation system; and there may be a lowerpressure drop in the CO₂ product stream producing line.

In another embodiment (hereinafter, the “third embodiment”) of themethod of the present invention:

-   -   the feed stream is introduced into the H₂/CO-PSA system;    -   the H₂/CO-PSA system separates the feed stream to provide the        H₂/CO product stream and a stream enriched in CO₂ and H₂S;    -   the further separation system separates said stream enriched in        CO₂ and H₂S to provide a stream further enriched in CO₂ and H₂S        and a stream comprising H₂ or H₂ and CO; and    -   the H₂S removal system processes said stream further enriched in        CO₂ and H₂S to provide the CO₂ product stream.

Further preferred features of this embodiment will again be apparentfrom the forgoing general description of the method.

As compared to the first embodiment, the method according to this thirdembodiment also has certain advantages and disadvantages. The advantagesare that, where a H₂S removal system is used that also produces an H₂Senriched stream, the H₂S concentration in this H₂S enriched stream islikely to be higher due to the removal of more H₂ or H₂ and CO upstreamof the H₂S removal system, and the loss of H₂ or H₂ and CO in the H₂Senriched stream should therefore also be reduced. The disadvantages arethat: the possibility of using the H₂S removal system to produce a driedfeed to the further separation system is removed, which may thereforenecessitate use of an additional TSA or other form of drying system thatis not negatively effected by the presence of H₂S in the stream; andthere will likely also be at least some H₂S present in the streamcomprising H₂ or H₂ and CO produced by the further separation system.

The apparatus of the invention may comprise:

-   -   an H₂/CO-PSA system for separating the feed stream to provide        the H₂/CO product stream and a stream enriched in CO₂ and H₂S;    -   a conduit arrangement for introducing the feed stream into the        H₂/CO-PSA system;    -   a conduit arrangement for withdrawing the H₂/CO product stream        from the H₂/CO-PSA system;    -   an H₂S removal system, for processing said stream enriched in        CO₂ and H₂S to provide a stream enriched in CO₂ and depleted in        H₂S;    -   a conduit arrangement for withdrawing the stream enriched in CO₂        and H₂S from the H₂/CO-PSA system and introducing the stream        into the H₂S removal system;    -   a further separation system, for separating said stream enriched        in CO₂ and depleted in H₂S to provide the CO₂ product stream and        a stream comprising H₂ or H₂ and CO;    -   a conduit arrangement for withdrawing the stream enriched in CO₂        and depleted in H₂S from the H₂S removal system and introducing        the stream into the further separation system;    -   a conduit arrangement for withdrawing the CO₂ product stream        from the further separation system; and    -   a conduit arrangement for withdrawing the stream comprising H₂        or H₂ and CO from the further separation system.

Alternatively, the apparatus of the invention may comprise:

-   -   an H₂S removal system, for processing the feed stream to provide        a stream depleted in H₂S;    -   a conduit arrangement for introducing the feed stream into the        H₂S removal system;    -   an H₂/CO-PSA system for separating said stream depleted in H₂S        to provide the H₂/CO product stream and a stream enriched in CO₂        and depleted in H₂S;    -   a conduit arrangement for withdrawing the stream depleted in H₂S        from the H₂S removal system and introducing the stream into the        H₂/CO-PSA system;    -   a conduit arrangement for withdrawing the H₂/CO product stream        from the H₂/CO-PSA system;    -   a further separation system, for separating said stream enriched        in CO₂ and depleted in H₂S to provide the CO₂ product stream and        a stream comprising H₂ or H₂ and CO;    -   a conduit arrangement for withdrawing the stream enriched in CO₂        and depleted in H₂S from the H₂/CO-PSA system and introducing        the stream into the further separation system;    -   a conduit arrangement for withdrawing the CO₂ product stream        from the further separation system; and    -   a conduit arrangement for withdrawing the stream comprising H₂        or H₂ and CO from the further separation system.

Alternatively, the apparatus of the invention may comprise:

-   -   an H₂/CO-PSA system for separating the feed stream to provide        the H₂/CO product stream and a stream enriched in CO₂ and H₂S;    -   a conduit arrangement for introducing the feed stream into the        H₂/CO-PSA system;    -   a conduit arrangement for withdrawing the H₂/CO product stream        from the H₂/CO-PSA system;    -   a further separation system, for separating said stream enriched        in CO₂ and H₂S to provide a stream further enriched in CO₂ and        H₂S and a stream comprising H₂ or H₂ and CO;    -   a conduit arrangement for withdrawing the stream enriched in CO₂        and H₂S from the H₂/CO-PSA system and introducing the stream        into the further separation system;    -   a conduit arrangement for withdrawing the stream comprising H₂        or H₂ and CO from the further separation system;    -   an H₂S removal system, for processing said stream further        enriched in CO₂ and H₂S to provide the CO₂ product stream;    -   a conduit arrangement for withdrawing the stream further        enriched in CO₂ and H₂S from the further separation system and        introducing the stream into the H₂S removal system; and    -   a conduit arrangement for withdrawing the CO₂ product stream        from the H₂S removal system.

Preferred features of these apparatus will be apparent from the forgoingdescription of the method.

Aspects of the invention include:

#1. A method for separating a feed stream, comprising H₂S, CO₂, H₂ andoptionally CO, into at least a CO₂ product stream and an H₂ or H₂ and COproduct stream (the “H₂/CO product stream”), wherein the feed stream isseparated using a pressure swing adsorption system (the “H₂/CO-PSAsystem”), an H₂S removal system, and a further separation system, andwherein:

-   -   the feed stream is introduced into either the H₂/CO-PSA system        or the H₂S removal system;    -   the H₂/CO-PSA system either separates the feed stream to provide        the H₂/CO product stream and a stream enriched in CO₂ and H₂S,        or separates a stream already depleted in H₂S by the H₂S removal        system to provide the H₂/CO product stream and a stream enriched        in CO₂ and depleted in H₂S;    -   the H₂S removal system either processes the feed stream to        provide a stream depleted in H₂S, or processes a stream already        enriched in CO₂ and H₂S by the H₂/CO-PSA system to provide a        stream enriched in CO₂ and depleted in H₂S, or processes a        stream already enriched in CO₂ and H₂S by the H₂/CO-PSA system        and further enriched in CO₂ and H₂S by the further separation        system to provide the CO₂ product stream; and    -   the further separation system either separates a stream already        enriched in CO₂ and H₂S by the H₂/CO-PSA system to provide a        stream further enriched in CO₂ and H₂S and a stream comprising        H₂ or H₂ and CO, or separates a stream already enriched in CO₂        by the H₂/CO-PSA system and depleted in H₂S by the H₂S removal        system to provide the CO₂ product stream and a stream comprising        H₂ or H₂ and CO.        #2. A method according to #1, wherein the H₂S removal system        separates the feed stream, or said stream already enriched in        CO₂ and H₂S by the H₂/CO-PSA system, or said stream already        enriched in CO₂ and H₂S by the H₂/CO-PSA system and further        enriched in CO₂ and H₂S by the further separation system, to        provide an H₂S enriched stream in addition to providing said        stream depleted in H₂S, said stream enriched in CO₂ and depleted        in H₂S, or said CO₂ product stream.        #3. A method according to #2, wherein the H₂S enriched stream        has a H₂S concentration of from about 20 to about 80 mol %.        #4. A method according to #2 or #3, wherein the H₂S removal        system is another pressure swing adsorption system (the        “sour-PSA system”).        #5. A method according to #4, wherein steam is used as a purge        gas for purging the sour-PSA.        #6. A method according to #4 or #5, wherein some or all of the        stream comprising H₂ or H₂ and CO obtained from the further        separation system is used as a purge gas for purging the        sour-PSA.        #7. A method according to any of #1 to #6, wherein some or all        of the stream comprising H₂ or H₂ and CO obtained from the        further separation system is recycled to the H₂/CO-PSA system        for further separation.        #8. A method according to any of #1 to #7, wherein some or all        of the stream comprising H₂ or H₂ and CO obtained from the        further separation system is combusted to generate power.        #9. A method according to any of #1 to #8, wherein some or all        of the stream comprising H₂ or H₂ and CO obtained from the        further separation system is combusted in the presence of        sufficient O₂ to convert all or substantially all of the H₂ and        CO in the part of the stream combusted to H₂O and CO₂.        #10. A method according to any of #1 to #9, wherein the further        separation system is a partial condensation system.        #11. A method according to any of #1 to #9, wherein the further        separation system is a membrane separation system.        #12. A method according to any of #1 to #11, wherein the feed        stream is formed from a sour syngas stream obtained from        gasification of solid or liquid carbonaceous feedstock.        #13. A method according to any of #1 to #12, wherein the feed        stream comprises from about 500 ppm to about 5 mole % H₂S, from        about 10 to about 60 mole % CO₂, and from about 35 mole % to the        remainder of H₂ or a mixture of H₂ and CO.        #14. A method according to any of #1 to #13, wherein at least        about 80% of the H₂ present in the feed stream is recovered in        the H₂/CO product stream and at most about 25% of the CO₂        present in the feed stream is recovered the H₂/CO product        stream, and wherein the H₂/CO product stream contains at most        about 50 ppm H₂S.        #15. A method according to any of #1 to #14, wherein at least        about 75% of the H₂ and CO present in the feed stream is        recovered the H₂/CO product stream and at most about 25% of the        CO₂ present in the feed stream is recovered the H₂/CO product        stream, and wherein the H₂/CO product stream contains at most        about 50 ppm H₂S.        #16. A method according to any of #1 to #15, wherein the CO₂        product stream has a CO₂ concentration of at least about 90 mole        % and contains at most about 100 ppm H₂S.        #17. A method according to any of #1 to #16, wherein:    -   the feed stream is introduced into the H₂/CO-PSA system;    -   the H₂/CO-PSA system separates the feed stream to provide the        H₂/CO product stream and a stream enriched in CO₂ and H₂S;    -   the H₂S removal system processes said stream enriched in CO₂ and        H₂S to provide a stream enriched in CO₂ and depleted in H₂S; and    -   the further separation system separates said stream enriched in        CO₂ and depleted in H₂S to provide the CO₂ product stream and a        stream comprising H₂ or H₂ and CO.        #18. A method according to #17, wherein feed stream further        comprises water, and the H₂S removal system processes said        stream enriched in CO₂ and H₂S to provide a stream enriched in        CO₂ and depleted in H₂S and water.        #19. A method according to any of #1 to #16, wherein:    -   the feed stream is introduced into the H₂S removal system;    -   the H₂S removal system processes the feed stream to provide a        stream depleted in H₂S;    -   the H₂/CO-PSA system separates said stream depleted in H₂S to        provide the H₂/CO product stream and a stream enriched in CO₂        and depleted in H₂S; and    -   the further separation system separates said stream enriched in        CO₂ and depleted in H₂S to provide the CO₂ product stream and a        stream comprising H₂ or H₂ and CO.        #20. A method according to any of #19, wherein feed stream        further comprises water, and the H₂S removal system processes        the feed stream to provide a stream depleted in H₂S and water.        #21. A method according to any of #1 to #16, wherein:    -   the feed stream is introduced into the H₂/CO-PSA system;    -   the H₂/CO-PSA system separates the feed stream to provide the        H₂/CO product stream and a stream enriched in CO₂ and H₂S;    -   the further separation system separates said stream enriched in        CO₂ and H₂S to provide a stream further enriched in CO₂ and H₂S        and a stream comprising H₂ or H₂ and CO;    -   the H₂S removal system processes said stream further enriched in        CO₂ and H₂S to provide the CO₂ product stream.        #22. Apparatus for separating a feed stream, comprising H₂S,        CO₂, H₂ and optionally CO, into at least a CO₂ product stream        and an H₂ or H₂ and CO product stream (the “H₂/CO product        stream”), the apparatus comprising:    -   a pressure swing adsorption system (the “H₂/CO-PSA system”) for        separating the feed stream to provide the H₂/CO product stream        and a stream enriched in CO₂ and H₂S;    -   a conduit arrangement for introducing the feed stream into the        H₂/CO-PSA system;    -   a conduit arrangement for withdrawing the H₂/CO product stream        from the H₂/CO-PSA system;    -   an H₂S removal system, for processing said stream enriched in        CO₂ and H₂S to provide a stream enriched in CO₂ and depleted in        H₂S;    -   a conduit arrangement for withdrawing the stream enriched in CO₂        and H₂S from the H₂/CO-PSA system and introducing the stream        into the H₂S removal system;    -   a further separation system, for separating said stream enriched        in CO₂ and depleted in H₂S to provide the CO₂ product stream and        a stream comprising H₂ or H₂ and CO;    -   a conduit arrangement for withdrawing the stream enriched in CO₂        and depleted in H₂S from the H₂S removal system and introducing        the stream into the further separation system;    -   a conduit arrangement for withdrawing the CO₂ product stream        from the further separation system; and    -   a conduit arrangement for withdrawing the stream comprising H₂        or H₂ and CO from the further separation system.        #23. Apparatus for separating a feed stream, comprising H₂S,        CO₂, H₂ and optionally CO, into at least a CO₂ product stream        and an H₂ or H₂ and CO product stream (the “H₂/CO product        stream”), the apparatus comprising:    -   an H₂S removal system, for processing the feed stream to provide        a stream depleted in H₂S;    -   a conduit arrangement for introducing the feed stream into the        H₂S removal system;    -   a pressure swing adsorption system (the “H₂/CO-PSA system”) for        separating said stream depleted in H₂S to provide the H₂/CO        product stream and a stream enriched in CO₂ and depleted in H₂S;    -   a conduit arrangement for withdrawing the stream depleted in H₂S        from the H₂S removal system and introducing the stream into the        H₂/CO-PSA system;    -   a conduit arrangement for withdrawing the H₂/CO product stream        from the H₂/CO-PSA system;    -   a further separation system, for separating said stream enriched        in CO₂ and depleted in H₂S to provide the CO₂ product stream and        a stream comprising H₂ or H₂ and CO;    -   a conduit arrangement for withdrawing the stream enriched in CO₂        and depleted in H₂S from the H₂/CO-PSA system and introducing        the stream into the further separation system;    -   a conduit arrangement for withdrawing the CO₂ product stream        from the further separation system; and    -   a conduit arrangement for withdrawing the stream comprising H₂        or H₂ and CO from the further separation system.        #24. Apparatus for separating a feed stream, comprising H₂S,        CO₂, H₂ and optionally CO, into at least a CO₂ product stream        and an H₂ or H₂ and CO product stream (the “H₂/CO product        stream”), the apparatus comprising:    -   a pressure swing adsorption system (the “H₂/CO-PSA system”) for        separating the feed stream to provide the H₂/CO product stream        and a stream enriched in CO₂ and H₂S;    -   a conduit arrangement for introducing the feed stream into the        H₂/CO-PSA system;    -   a conduit arrangement for withdrawing the H₂/CO product stream        from the H₂/CO-PSA system;    -   a further separation system, for separating said stream enriched        in CO₂ and H₂S to provide a stream further enriched in CO₂ and        H₂S and a stream comprising H₂ or H₂ and CO;    -   a conduit arrangement for withdrawing the stream enriched in CO₂        and H₂S from the H₂/CO-PSA system and introducing the stream        into the further separation system;    -   a conduit arrangement for withdrawing the stream comprising H₂        or H₂ and CO from the further separation system;    -   an H₂S removal system, for processing said stream further        enriched in CO₂ and H₂S to provide the CO₂ product stream;    -   a conduit arrangement for withdrawing the stream further        enriched in CO₂ and H₂S from the further separation system and        introducing the stream into the H₂S removal system; and    -   a conduit arrangement for withdrawing the CO₂ product stream        from the H₂S removal system.

Solely by way of example, certain embodiments of the invention will nowbe described with reference to the accompanying drawings.

Referring to FIG. 1, a feed stream (1) is fed to a H₂/CO-PSA system(101) at 6 MPa (60 bar) absolute. The composition of the feed stream is1.0 mol % H₂S, 39.0 mol % CO₂ and 60.0 mol % of a mixture of H₂ and CO(figures rounded to the nearest 0.1 mol %). The H₂/CO-PSA system (101)separates the feed (1) into a H₂ and CO product stream (2) and a stream(3) enriched in CO₂ and H₂S. The H₂ and CO product stream (2) isproduced at 6 MPa (60 bar) absolute, and is 6.1 mol % CO₂ and 93.9 mol %H₂ and CO. The CO₂ and H₂S enriched stream (3) is produced at 0.1 MPa (1bar) absolute, and is 2.0 mol % H₂S, 77.0 mol % CO₂, and 21.0 mol % H₂and CO.

The H₂ and CO product stream (2) can be sent for combustion andexpansion of the resulting combustion effluent in a gas turbine (notshown) or used for chemicals production in a chemicals plant (notshown). The CO₂ and H₂S enriched stream (3) is sent to a compressor(102) and compressed to 3.1 MPa (31 bar) absolute. The compressed CO₂and H₂S enriched stream (4) is then introduced into a sour-PSA system(103) where it is separated into an H₂S enriched stream (7) and a H₂Sdepleted, CO₂ enriched stream (5).

The H₂S enriched stream (7), produced at 0.1 MPa (1 bar) absolute, is40.0 mol % H₂S and 60.0 mol % CO₂ (it may include trace amounts ofH₂/CO) and can be sent to a sulphur recovery system, such as for examplea Claus plant (not shown), for conversion of the H₂S into elementalsulphur.

The stream depleted in H₂S and enriched in CO₂ (5), which is produced at3.1 MPa (31 bar) absolute, is 77.8 mol % CO₂ and 22.2 mol % H₂ and COand is transferred to a partial condensation system (104) where it iscooled to about −55° C. to partially condense the stream. The partiallycondensed stream is then separated, using one or more flash drums (phaseseparators) and/or distillation columns into a liquid further enrichedin CO₂ and vapour comprising CO₂, H₂ and CO. Due to the vapour pressureof CO₂ at −55° C., the vapour is 25.0 mol % CO₂, the remainder (i.e.75.0 mol %) being H₂ and CO. No compression of the of the H₂S depleted,CO₂ enriched stream (5) is, in the depicted flow sheet, required priorto introduction of the stream into the partial condensation system(104), although if this stream were to be produced at a lower pressurethan that required of the feed to the partial condensation system then afurther compressor could be added between the sour-PSA system (103) andpartial condensation system (104).

The liquid condensate, which is 99.0 mol % CO₂ and 1.0 mol % H₂ and CO,is withdrawn from the partial condensation system (104) as CO₂ productstream (6). This stream may be pumped to another location in its liquidstate, or it may be vaporized and compressed in a further compressor(105) to a sufficient pressure, such as 12 MPa (120 bar) absolute, to bepiped as a stream (9) to a geological storage site or used for EOR.

The vapour comprising CO₂, H₂ and CO is withdrawn as gas stream (8), at3 MPa (30 bar) absolute, and can be used in a number of ways or simplydisposed of. For example, a portion or all of this gas stream may bevented (not shown), used as feed to some other process (not shown),admixed with the H₂/CO-product stream (2) from the H₂/CO-PSA system(101) (not shown), compressed in another compressor (106) and recycledto the H₂/CO-PSA system (101) by being added to the process feed (1) (asshown by the dashed line in FIG. 1), used as a purge gas for thesour-PSA system (103) (not shown), or recycled to the partialcondensation system (104) for further separation (not shown).

The H₂/CO-PSA system (101) and sour-PSA system (103) may be operatedusing any of a variety of different PSA cycles, as will be well known toone of ordinary skill in the art.

For example, referring to FIG. 2 and Table 1, the sour-PSA system (103)may comprise 8 beds, arranged in parallel and designated in FIG. 2 as Ato H. Each bed undergoes a PSA cycle involving the following steps inthe following order: feed; rinse; equalization; provide purge;blowdown/depressurization; purge; equalization; repressurisation (oneequalization step is shown, although more may be used in practice). Thecycles of the beds are staggered as shown in FIG. 2 and described inTable 1, wherein at the point in time depicted in FIG. 2:

bed A is undergoing feed with the CO₂ and H₂S enriched stream (4) andadsorbing H₂S;

bed B is undergoing rinse using a portion of the H₂S gases obtained frombeds E and F, the gas pushed through bed B being combined with the gaspushed through from bed A to provide the H₂S depleted, CO₂ enrichedstream (5);

bed C is providing equalization gas to bed G;

bed D is providing a CO₂ enriched purge gas to bed F;

bed E is undergoing blowdown, the gas obtained being combined with thegas obtained from bed F;

bed F is undergoing purge with CO₂ enriched purge gas from bed D, thecombined gases obtained from beds E and F being combined to provide theH₂S enriched stream (7) and the rinse gas to bed B;

bed G is receiving equalization gas from bed C; and

bed H is undergoing repressurisation, using a portion of the CO₂ and H₂Senriched stream (4).

Referring to FIG. 3 and Table 2, an alternative PSA cycle is shown,wherein the sour-PSA system (103) comprises 9 beds, arranged in paralleland designated in FIG. 4 as I to Q. Each bed goes undergoes a PSA cycleinvolving the following steps in the following order: feed;equalization; provide purge; rinse; blowdown/depressurization; purge;accept rinse; equalization; repressurisation. The cycles of the beds arestaggered as shown in FIG. 3 and further described in Table 2.

Referring to FIG. 4 and Table 3, another PSA cycle is shown, wherein thesour-PSA system (103) comprises 8 beds, arranged in parallel anddesignated in FIG. 4 as R to Y. Each bed goes undergoes a PSA cycleinvolving the following steps in the following order: feed;equalization; provide purge; rinse; blowdown/depressurization; purge;equalization; repressurisation. The cycles of the beds are staggered asshown in FIG. 4 and further described in Table 3.

TABLE 1 End of Step Pressure Pro- (bar duct Bed Step absolute) Feed GasGas A Feed 31 CO₂ & H₂S CO₂ B Rinse (combine with product gas) 31 H₂SCO₂ C Equalisation 16 — CO₂ D Provide CO₂ Purge 10 — CO₂ EBlowdown/Depressurisation 1 — H₂S F Purge with CO₂ 1 CO₂ H₂S GEqualisation 16 CO₂ — H Repressurisation with Product 31 CO₂ —

TABLE 2 End of Step Pressure (bar Product Bed Step absolute) Feed GasGas I Feed 31 CO₂ & H₂S CO₂ J Equalisation 18 — CO₂ K Provide CO₂ Purge12 — CO₂ L Rinse (to another vessel) 12 H₂S CO₂ MBlowdown/Depressurisation 1 _(—) H₂S N Purge 1 CO₂ H₂S O Accept RinseGas 5 CO₂ — P Equalisation 18 CO₂ — Q Repressurisation with Product 31CO₂ —

TABLE 3 End of Step Pressure (bar Product Bed Step absolute) Feed GasGas R Feed 31 CO₂ & H₂S CO₂ S Equalisation 16 — CO₂ T Provide CO₂ Purge10 — CO₂ U Rinse (combine product gases) 10 H₂S CO₂ VBlowdown/Depressurisation 1 — H₂S W Purge 1 CO₂ H₂S X Equalisation 16CO₂ — Y Repressurisation with Product 31 CO₂ —

Referring to FIG. 5, a flow sheet depicting an alternative embodiment ofthe invention is shown, in which the same reference numerals have beenused as in FIG. 1 to denote common features. In this embodiment the feedstream (1) is fed, at 3 MPa (30 bar) absolute, to sour-PSA system (103).The composition of the feed stream (1) is again 1.0 mol % H₂S, 39.0 mol% CO₂ and 60.0 mol % of a mixture of H₂ and CO (figures rounded to thenearest 0.1 mol %).

The sour-PSA system (103) separates the feed (1) into an H₂S enrichedstream (7) and a H₂S depleted stream (25). The H₂S enriched stream (7),produced at 0.1 MPa (1 bar) absolute, is 25.0 mol % H₂S and 75.0 mol %CO₂ and may, again, be sent to a sulphur recovery system (not shown) forconversion of the H₂S into elemental sulphur. The H₂S depleted stream(21) is produced at 3 MPa (30 bar) absolute, and is 37.5 mol % CO₂ and62.5 mol % H₂ and CO.

The H₂S depleted stream (21) is transferred to H₂/CO-PSA system (101)which separates the H₂S depleted stream (21) into an H₂ and CO productstream (2) and a stream (22) enriched in CO₂ (and which remains depletedin H₂S). In the flow sheet depicted the H₂S depleted stream (21) is notfurther compressed prior to being introduced into the H₂/CO-PSA system(101), but further compression could of course be provided if required.The H₂ and CO product stream (2) is produced at the same pressure as theH₂S depleted stream (25), i.e. 3 MPa (30 bar) absolute, and is again 6.1mol % CO₂ and 93.9 mol % H₂ and CO. The CO₂ enriched and H₂S depletedstream (22) is produced at 0.1 MPa (1 bar) absolute, and is 77.1 mol %CO₂, and 22.9 mol % H₂ and CO.

The H₂ and CO product stream (2) can, as discussed above, be sent forcombustion and expansion of the resulting combustion effluent in a gasturbine (not shown) or used for chemicals production in a chemicalsplant (not shown). The CO₂ enriched and H₂S depleted stream (22) is sentto a compressor (201) and compressed to 3.0 MPa (30 bar) absolute. Thecompressed CO₂ enriched and H₂S depleted stream (23) is then introducedinto partial condensation system (104).

Partial condensation system (104) cools the compressed CO₂ enriched andH₂S depleted stream (23) to about −55° C. to partially condense thestream. The partially condensed stream is then separated, using one ormore flash drums (phase separators) and/or distillation columns into aliquid further enriched in CO₂ and vapour comprising CO₂, H₂ and CO. Dueto the vapour pressure of CO₂ at −55° C., the vapour is 25.0 mol % CO₂,the remainder (i.e. 75.0 mol %) being H₂ and CO.

The liquid condensate, which is 99.0 mol % CO₂ and 1.0 mol % H₂ and CO,is withdrawn from the partial condensation system (104) as CO₂ productstream (6). This stream may again be pumped to another location in itsliquid state, or vaporized and compressed in a further compressor (105)to a sufficient pressure, such as 12 MPa (120 bar) absolute, to be pipedas a stream (9) to a geological storage site or used for EOR.

The vapour comprising CO₂, H₂ and CO is withdrawn as gas stream (8), at3 MPa (30 bar) absolute, and can again be used in a number of ways orsimply disposed of, as discussed above. In the flow sheet depicted inFIG. 5, the gas stream is recycled to the H₂/CO-PSA system (101) bybeing added to the H₂S depleted stream (21) (as shown by the dashed linein FIG. 5).

The H₂/CO-PSA system (101) and sour-PSA system (103) may again beoperated using any of a variety of different PSA cycles, as will be wellknown to one of ordinary skill in the art. The sour-PSA system (103)may, for example, be operated via any of the cycles described above withreference to FIGS. 2 to 4.

Referring to FIG. 6, a flow sheet depicting another embodiment of theinvention is shown, in which the same reference numerals have again beenused as in FIG. 1 to denote common features. In this embodiment, feedstream (1) is once more fed, at 6 MPa (60 bar) absolute, to H₂/CO-PSAsystem (101). The composition of the feed stream is again 1.0 mol % H₂S,39.0 mol % CO₂ and 60.0 mol % of a mixture of H₂ and CO (figures roundedto the nearest 0.1 mol %). The H₂/CO-PSA system (101) separates the feed(1) into a H₂ and CO product stream (2) and a stream (3) enriched in CO₂and H₂S. The H₂ and CO product stream (2) is produced at 6 MPa (60 bar)absolute, and is 6.1 mol % CO₂ and 93.9 mol % H₂ and CO. The CO₂ and H₂Senriched stream (3) is produced at 0.1 MPa (1 bar) absolute, and is 2.2mol % H₂S, 76.8 mol % CO₂, and 21.1 mol % H₂ and CO.

The H₂ and CO product stream (2) can, as discussed above, be sent forcombustion and expansion of the resulting combustion effluent in a gasturbine (not shown) or used for chemicals production in a chemicalsplant (not shown). The CO₂ and H₂S enriched stream (3) is sent to acompressor (102) and compressed to 3.0 MPa (30 bar) absolute. Thecompressed CO₂ and H₂S enriched stream (4) is then introduced intopartial condensation system (104).

Partial condensation system (104) cools the compressed CO₂ and H₂Senriched stream (4) to about −55° C. to partially condense the stream.The partially condensed stream is then separated, using one or moreflash drums (phase separators) and/or distillation columns into a liquidfurther enriched in CO₂ and H₂S and a vapour comprising H₂S, CO₂, H₂ andCO. Due to the vapour pressure of H₂S and CO₂ at −55° C., the vapour is0.6 mol % H₂S, 25.0 mol % CO₂ and 74.4 mol % H₂ and CO.

The vapour comprising H₂S, CO₂, H₂ and CO is withdrawn as gas stream(32), at 3 MPa (30 bar) absolute, and can again be used in a number ofways or simply disposed of, as discussed above. In the flow sheetdepicted in FIG. 6, the gas stream is compressed in another compressor(106) and recycled to the H₂/CO-PSA system (101) by being added to theprocess feed (1) (as shown by the dashed line in FIG. 6).

The liquid condensate, which is 2.8 mol % H₂S, 96.3 mol % CO₂ and 0.9mol % H₂ and CO, is vaporized and is withdrawn from the partialcondensation system (104) as stream (31) at 3 MPa (30 bar) absolute.This stream is sent to sour-PSA system (103) where it is separated intoan H₂S enriched stream (7) and the CO₂ product stream (6). In the flowsheet depicted the further enriched in CO₂ and H₂S stream (31) is notfurther compressed prior to being introduced into the H₂/CO-PSA system(101), but further compression could of course be provided if required.

The H₂S enriched stream (7), produced at 0.1 MPa (1 bar) absolute by thesour-PSA system (103), is 50.0 mol % H₂S and 50.0 mol % CO₂ and canagain be sent to a sulphur recovery system (not shown) for conversion ofthe H₂S into elemental sulphur. The CO₂ product stream (6), which is99.0 mol % CO₂ and 1.0 mol % H₂ and CO, is withdrawn from the sour-PSAsystem (103) at 30 MPa (1 bar) and may be compressed in a furthercompressor (105) to a sufficient pressure, such as 12 MPa (120 bar)absolute, to be piped as a stream (9) to a geological storage site orused for EOR.

The H₂/CO-PSA system (101) and sour-PSA system (103) may again beoperated using any of a variety of different PSA cycles, as will be wellknown to one of ordinary skill in the art. The sour-PSA system (103)may, for example, be operated via any of the cycles described above withreference to FIGS. 2 to 4.

It will be appreciated that the invention is not restricted to thedetails described above with reference to the preferred embodiments butthat numerous modifications and variations can be made without departingform the spirit or scope of the invention as defined in the followingclaims.

1. A method for separating a feed stream, comprising at least H₂S, COand H₂, into at least a CO₂ product stream and an H₂ or H₂ and COproduct stream (the “H₂/CO product stream”), wherein the feed stream isformed from a sour syngas stream obtained from gasification of a solidor liquid carbonaceous feedstock and is separated using a pressure swingadsorption system (the “H₂/CO-PSA system”), an H₂S removal system, and afurther separation system, and wherein: the feed stream is introducedinto either the H₂/CO-PSA system or the H₂S removal system; theH₂/CO-PSA system either separates the feed stream to provide the H₂/COproduct stream and a stream enriched in CO₂ and H₂S, or separates astream already depleted in H₂S by the H₂S removal system to provide theH₂/CO product stream and a stream enriched in CO₂ and depleted in H₂S;the H₂S removal system either processes the feed stream to provide astream depleted in H₂S, or processes a stream already enriched in CO₂and H₂S by the H₂/CO-PSA system to provide a stream enriched in CO₂ anddepleted in H₂S, or processes a stream already enriched in CO₂ and H₂Sby the H₂/CO-PSA system and further enriched in CO₂ and H₂S by thefurther separation system to provide the CO₂ product stream; and thefurther separation system either separates a stream already enriched inCO₂ and H₂S by the H₂/CO-PSA system to provide a stream further enrichedin CO₂ and H₂S and a stream comprising H₂ or H₂ and CO, or separates astream already enriched in CO₂ by the H₂/CO-PSA system and depleted inH₂S by the H₂S removal system to provide the CO₂ product stream and astream comprising H₂ or H₂ and CO.
 2. The method of claim 1, wherein theH₂S removal system separates the feed stream, or said stream alreadyenriched in CO₂ and H₂S by the H₂/CO-PSA system, or said stream alreadyenriched in CO₂ and H₂S by the H₂/CO-PSA system and further enriched inCO₂ and H₂S by the further separation system, to provide an H₂S enrichedstream in addition to providing said stream depleted in H₂S, said streamenriched in CO₂ and depleted in H₂S, or said CO₂ product stream.
 3. Themethod of claim 2, wherein the H₂S removal system is another pressureswing adsorption system (the “sour-PSA system”).
 4. The method of claim1, wherein the further separation system is a partial condensationsystem.
 5. The method of claim 1, wherein the further separation systemis a membrane separation system.
 6. The method of claim 1, wherein thefeed stream comprises from about 500 ppm to about 5 mole % H₂S, fromabout 10 to about 60 mole % CO₂, and from about 35 mole % to theremainder of H₂ or a mixture of H₂ and CO.
 7. The method of claim 1,wherein at least about 80% of the H₂ present in the feed stream isrecovered in the H₂/CO product stream and at most about 25% of the CO₂present in the feed stream is recovered the H₂/CO product stream, andwherein the H₂/CO product stream contains at most about 50 ppm H₂S. 8.The method of claim 1, wherein at least about 75% of the H₂ and COpresent in the feed stream is recovered the H₂/CO product stream and atmost about 25% of the CO₂ present in the feed stream is recovered theH₂/CO product stream, and wherein the H₂/CO product stream contains atmost about 50 ppm H₂S.
 9. The method of claim 1, wherein the CO₂ productstream has a CO₂ concentration of at least about 90 mole % and containsat most about 100 ppm H₂S.
 10. The method of claim 2, wherein the H₂Senriched stream has a H₂S concentration of from about 20 to about 80 mol%.
 11. The method of claim 1, wherein some or all of the streamcomprising H₂ or H₂ and CO obtained from the further separation systemis recycled to the H₂/CO-PSA system for further separation.
 12. Themethod of claim 1, wherein some or all of the stream comprising H₂ or H₂and CO obtained from the further separation system is combusted togenerate power.
 13. The method of claim 1, wherein some or all of thestream comprising H₂ or H₂ and CO obtained from the further separationsystem is combusted in the presence of sufficient O₂ to convert all orsubstantially all of the H₂ and CO in the part of the stream combustedto H₂O and CO₂.
 14. The method of claim 3, wherein steam is used as apurge gas for purging the sour-PSA.
 15. The method of claim 3, whereinsome or all of the stream comprising H₂ or H₂ and CO obtained from thefurther separation system is used as a purge gas for purging thesour-PSA.
 16. The method of claim 1, wherein: the feed stream isintroduced into the H₂/CO-PSA system; the H₂/CO-PSA system separates thefeed stream to provide the H₂/CO product stream and a stream enriched inCO₂ and H₂S; the H₂S removal system processes said stream enriched inCO₂ and H₂S to provide a stream enriched in CO₂ and depleted in H₂S; andthe further separation system separates said stream enriched in CO₂ anddepleted in H₂S to provide the CO₂ product stream and a streamcomprising H₂ or H₂ and CO.
 17. The method of claim 16, wherein feedstream further comprises water, and the H₂S removal system processessaid stream enriched in CO₂ and H₂S to provide a stream enriched in CO₂and depleted in H₂S and water.
 18. The method of claim 1, wherein: thefeed stream is introduced into the H₂S removal system; the H₂S removalsystem processes the feed stream to provide a stream depleted in H₂S;the H₂/CO-PSA system separates said stream depleted in H₂S to providethe H₂/CO product stream and a stream enriched in CO₂ and depleted inH₂S; and the further separation system separates said stream enriched inCO₂ and depleted in H₂S to provide the CO₂ product stream and a streamcomprising H₂ or H₂ and CO.
 19. The method of claim 18, wherein feedstream further comprises water, and the H₂S removal system processes thefeed stream to provide a stream depleted in H₂S and water.
 20. Themethod of claim 1, wherein: the feed stream is introduced into theH₂/CO-PSA system; the H₂/CO-PSA system separates the feed stream toprovide the H₂/CO product stream and a stream enriched in CO₂ and H₂S;the further separation system separates said stream enriched in CO₂ andH₂S to provide a stream further enriched in CO₂ and H₂S and a streamcomprising H₂ or H₂ and CO; the H₂S removal system processes said streamfurther enriched in CO₂ and H₂S to provide the CO₂ product stream. 21.Apparatus for separating a feed stream, formed from a sour syngas streamobtained from gasification of a solid or liquid carbonaceous feedstockand comprising at least H₂S, CO₂ and H₂, into at least a CO₂ productstream and an H₂ or H₂ and CO product stream (the “H₂/CO productstream”), the apparatus comprising: a pressure swing adsorption system(the “H₂/CO-PSA system”) for separating the feed stream to provide theH₂/CO product stream and a stream enriched in CO₂ and H₂S; a conduitarrangement for introducing the feed stream into the H₂/CO-PSA system; aconduit arrangement for withdrawing the H₂/CO product stream from theH₂/CO-PSA system; an H₂S removal system, for processing said streamenriched in CO₂ and H₂S to provide a stream enriched in CO₂ and depletedin H₂S; a conduit arrangement for withdrawing the stream enriched in CO₂and H₂S from the H₂/CO-PSA system and introducing the stream into theH₂S removal system; a further separation system, for separating saidstream enriched in CO₂ and depleted in H₂S to provide the CO₂ productstream and a stream comprising H₂ or H₂ and CO; a conduit arrangementfor withdrawing the stream enriched in CO₂ and depleted in H₂S from theH₂S removal system and introducing the stream into the furtherseparation system; a conduit arrangement for withdrawing the CO₂ productstream from the further separation system; and a conduit arrangement forwithdrawing the stream comprising H₂ or H₂ and CO from the furtherseparation system.
 22. Apparatus for separating a feed stream, formedfrom a sour syngas stream obtained from gasification of a solid orliquid carbonaceous feedstock and comprising at least H₂S, CO₂ and H₂,into at least a CO₂ product stream and an H₂ or H₂ and CO product stream(the “H₂/CO product stream”), the apparatus comprising: an H₂S removalsystem, for processing the feed stream to provide a stream depleted inH₂S; a conduit arrangement for introducing the feed stream into the H₂Sremoval system; a pressure swing adsorption system (the “H₂/CO-PSAsystem”) for separating said stream depleted in H₂S to provide the H₂/COproduct stream and a stream enriched in CO₂ and depleted in H₂S; aconduit arrangement for withdrawing the stream depleted in H₂S from theH₂S removal system and introducing the stream into the H₂/CO-PSA system;a conduit arrangement for withdrawing the H₂/CO product stream from theH₂/CO-PSA system; a further separation system, for separating saidstream enriched in CO₂ and depleted in H₂S to provide the CO₂ productstream and a stream comprising H₂ or H₂ and CO; a conduit arrangementfor withdrawing the stream enriched in CO₂ and depleted in H₂S from theH₂/CO-PSA system and introducing the stream into the further separationsystem; a conduit arrangement for withdrawing the CO₂ product streamfrom the further separation system; and a conduit arrangement forwithdrawing the stream comprising H₂ or H₂ and CO from the furtherseparation system.
 23. Apparatus for separating a feed stream, formedfrom a sour syngas stream obtained from gasification of a solid orliquid carbonaceous feedstock and comprising at least H₂S, CO₂ and H₂,into at least a CO₂ product stream and an H₂ or H₂ and CO product stream(the “H₂/CO product stream”), the apparatus comprising: a pressure swingadsorption system (the “H₂/CO-PSA system”) for separating the feedstream to provide the H₂/CO product stream and a stream enriched in CO₂and H₂S; a conduit arrangement for introducing the feed stream into theH₂/CO-PSA system; a conduit arrangement for withdrawing the H₂/COproduct stream from the H₂/CO-PSA system; a further separation system,for separating said stream enriched in CO₂ and H₂S to provide a streamfurther enriched in CO₂ and H₂S and a stream comprising H₂ or H₂ and CO;a conduit arrangement for withdrawing the stream enriched in CO₂ and H₂Sfrom the H₂/CO-PSA system and introducing the stream into the furtherseparation system; a conduit arrangement for withdrawing the streamcomprising H₂ or H₂ and CO from the further separation system; an H₂Sremoval system, for processing said stream further enriched in CO₂ andH₂S to provide the CO₂ product stream; a conduit arrangement forwithdrawing the stream further enriched in CO₂ and H₂S from the furtherseparation system and introducing the stream into the H₂S removalsystem; and a conduit arrangement for withdrawing the CO₂ product streamfrom the H₂S removal system.